Inkjet printing mechanisms use pens which shoot drops of liquid colorant, referred to generally herein as "ink," onto a page. Each pen has a printhead formed with very small nozzles through which the ink drops are fired. To print an image, the printhead is propelled back and forth across the page, shooting drops of ink in a desired pattern as it moves. The particular ink ejection mechanism within the printhead may take on a variety of different forms known to those skilled in the art, such as those using piezo-electric or thermal printhead technology. For instance, two earlier thermal ink ejection mechanisms are shown in U.S. Pat. Nos. 5,278,584 and 4,683,481, both assigned to the present assignee, Hewlett-Packard Company. In a thermal system, a barrier layer containing ink channels and vaporization chambers is located between a nozzle orifice plate and a substrate layer. This substrate layer typically contains linear arrays of heater elements, such as resistors, which are energized to heat ink within the vaporization chambers. Upon heating, an ink droplet is ejected from a nozzle associated with the energized resistor. By selectively energizing the resistors as the printhead moves across the page, the ink is expelled in a pattern on the print media to form a desired image (e.g., picture, chart or text).
To clean and protect the printhead, typically a "service station" mechanism is mounted within the printer chassis so the printhead can be moved over the station for maintenance. For storage, or during non-printing periods, the earlier service stations used a capping system having an elastomeric sealing cup with a lip which surrounded the printhead nozzles to form a seal that protects the nozzles from contaminants and from drying. To facilitate priming, some printers had priming caps that are connected to a pumping unit to draw a vacuum on the printhead. During operation, partial occlusions or clogs in the printhead are periodically cleared by firing a number of drops of ink through each of the nozzles in a clearing or purging process known as "spitting." The waste ink is collected at a spitting reservoir portion of the service station, known as a "spittoon." After spitting, uncapping, or occasionally during printing, most service stations clean the printhead using a flexible wiper that wipes the printhead surface to remove ink residue, as well as any paper dust or other debris that has collected on the printhead.
To improve the clarity and contrast of the printed image, recent research has focused on improving the ink itself. To provide quicker, more waterfast printing with darker blacks and more vivid colors, pigment based inks have been developed. These pigment based inks have a higher solids content than the earlier dye-based inks, which results in a higher optical density for the new inks. Both types of ink dry quickly, which allows inkjet printing mechanisms to use plain paper. Unfortunately, the combination of small nozzles and quick-drying ink leaves the printheads susceptible to clogging, not only from dried ink and minute dust particles or paper fibers, but also from the solids within the new inks themselves. Partially or completely blocked nozzles can lead to either missing or misdirected drops on the print media, either of which degrades the print quality. Thus, spitting to clear the nozzles becomes even more important when using pigment-based inks, because the higher solids content contributes to the clogging problem more than the earlier dye-based inks.
In the past, the printhead wipers have typically been a single or dual wiper blade made of an elastomeric material. Typically, the printhead is translated across the wiper in a direction parallel to the scan axis of the printhead, so for a pen having nozzles aligned in two linear arrays perpendicular to the scanning axis, first one row of nozzles was wiped and then the other row was wiped. A revolutionary orthogonal wiping scheme was used in the Hewlett-Packard Company's DeskJet.RTM. 850C, 855C, 820C and 870C color inkjet printer models, where the wipers ran along the length of the linear arrays, wicking ink from one nozzle to the next. This wicked ink acted as a solvent to break down ink residue accumulated on the nozzle plate. This product also used a dual wiper blade system, with special contours on the wiper blade tip to facilitate the wicking action and subsequent cleaning.
Challenges were faced in finding suitable capping strategies for the new pigment based inks, while also adequately capping the multi-color dye based printhead. Earlier capping systems placed a sealing chamber around the nozzles to hermetically seal the printhead nozzles in a humidified atmospheric environment that prevented drying or decomposition of the ink during periods of printer inactivity. Once again, the Hewlett-Packard Company's DeskJet.RTM. 850C, 855C, 820C and 870C color inkjet printers employed an elastomeric capping chamber with a unique multi-ridged lip to seal the pigment based black pen. A spring-biased rocking sled supported both the black and color caps, and gently engaged the printheads to avoid depriming them. A unique vent system comprising a Santoprene.RTM. cap plug and a labyrinth vent path under the sled avoided inadvertent deprimes, while also accommodating barometric changes in the ambient pressure. While the radically new service station first employed in the DeskJet.RTM. 850C printer, and later in the DeskJet.RTM. 855C, 820C and 870C printer models, addressed a myriad of problems encountered with the new pigment based inks, this service station had drawbacks. For instance, the capping assembly, as well as the priming system, had numerous moving parts so the service station required a series of intricate manufacturing steps for assembly.